Apparatus for generating a rotating laser beam

ABSTRACT

The present invention relates to an apparatus ( 1 ) for generating a rotating laser beam ( 5 ) which may used for various applications including welding, cutting, drilling or ablation of materials. More particularly, the apparatus according to the present invention is able to produce a fast rotating and accurate laser beam, because the main optical device ( 100 ) that is rotated consists of a first reflecting surface ( 102 ) rotating about an axis (X 1 ) at least a second reflecting surface ( 26 ), said first reflecting surface ( 102 ) intented to redirect said laser beam into the direction of the second reflecting surface ( 26 ), and a rotating lens ( 107 ) of optical axis (X 2 ) arranged to be tiltable, such that said optical axis (X 2 ) is able to be angled with respect to said axis (X 1 ).

FIELD OF THE INVENTION

The present invention relates to an apparatus for generating a rotatinglaser beam and, more particularly, to such an apparatus allowingaccurate and fast circular machining and/or welding. Such an apparatuscan also advantageously be applied to the visioning of circularmachining and/or welding regions.

BACKGROUND OF THE INVENTION

Although the following description relates specifically to a weldingapparatus, it must be understood that, depending on the laser beamparameters, the apparatus according to the present invention can alsobeen used for machining operations, such as cutting, drilling orablation of materials.

Systems for circular welding with a laser beam, for example, are knownfrom the prior art.

Some of these systems are based on the principle that the weldingapparatus is arranged with respect to one or more workpieces to bewelded in a stationary manner. The laser beam is directed to a weldingregion of the workpieces in a fixed direction, whereas the workpiecesare driven in rotation by a support comprising motor means for thatpurpose.

However, such systems present many drawbacks in that it is difficult toprecisely adjust the position of the workpiece with respect to the laserbeam, this being especially critical when the workpiece is rotated at ahigh speed of rotation.

Further, the corresponding welding process takes a long time if thereare a large number of workpieces to be welded successively. Indeed, inthe process, the workpiece has to be positioned in its still supportbefore the latter is driven in rotation with a high speed. Then thewelding treatment is applied as soon as the workpiece is rotated fasterthan a predetermined rotating speed. After the welding treatment, thesupport has to stop rotating before the workpiece is removed from it andbefore the next workpiece is positioned.

Other systems are known, in which the workpiece remains still during thewelding process, the laser beam direction being changed to sweep thewhole welding region. In order to cover the whole welding region withthe laser beam, two mirrors are arranged in the optical path of thelaser beam so that they can be tilted independently of each other, eachbetween two end positions. Thus, one of the mirrors is responsible for amovement of the laser beam along a first direction X-X′ while the secondmirror is responsible for a movement of the laser beam along a seconddirection Y-Y′, perpendicular to the first direction X-X′. Consequently,the combination of the respective tilts of the two mirrors covers thewhole welding region of the workpiece.

However, a drawback of such systems is that the larger the dimensions ofthe welding region, the further the end positions are from one anotherfor each of the mirrors. Thus, the time necessary for a mirror to tiltfrom one end position to the other is longer, which leads to a decreasein the overall speed of the welding process.

Futher, JP 60-236482A in the name of Mitsubishi Electric Corp. andpublished on Nov. 25, 1985, discloses an apparatus for generating arotating laser beam comprising a large focal length lens standing in astill position as regards the apparatus and a first reflecting surfacemounted on a rotating support for being driven in rotation. The lightreflected by the first reflecting surface is directed toward a secondreflecting surface and then toward a third reflecting surface.

However, all three reflecting surfaces described in this document are ofplanar shape in cross-section and introduce thus an error in the shapeof the image focus point formed on the workpiece to be welded, as theyare combined with a large focal length lens.

SUMMARY OF THE INVENTION

A first object of the present invention is to improve the systems of theaforementioned prior art by providing an apparatus for performing acircular machining on at least one workpiece in a fast and reliablemanner.

Thus, the present invention concerns such an apparatus comprising meansfor supplying a laser beam, said laser beam following an optical paththrough at least one optical system of the apparatus before emergingfrom said apparatus through an output before impinging onto an impactregion of the workpiece. The optical system presents a central axis X1and is at least intended to adjust the position of an image focal pointof said laser beam in the impact region. The optical system furthercomprises a first reflecting surface able to rotate with respect to thecentral axis X1 and intended to redirect the laser beam into thedirection of at least a second reflecting surface intended to reflectthe laser beam towards the workpieces. The apparatus is characterised bythe fact that it comprises means to drive the first reflecting surfacetogether with the optical system in rotation. The apparatus according tothe present invention is further characterised by the fact that theoptical system comprises a rotating lens of optical axis X2 arranged soas to be tiltable, such that the optical axis X2 is able to be angledwith respect to the central axis X1, to increase the quality of theimage focus point on the workpiece.

Thus, circular machining, welding for example, can be obtained by asimple rotational movement of a reflecting surface, allowing theimplementation of high rotational speeds, the rotational speed beingindependent of the dimensions of the welding.

Owing to its tiltable lens which is rotating together with the firstreflecting surface, the quality of the image focus point on theworkpiece can be finely adjusted. This last feature is thus an importantadditional improvement as regards the above mentioned known systems, inthat with the latter no adjustment of the quality of the laser beam isprovided, such adjustment taking into account the motion of thereflective surface.

According to a preferred embodiment of the present invention, the firstreflecting surface is arranged in a stationary manner in the opticalsystem, the latter being able to rotate with respect to the central axisX1 via the action of said motor means.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described in more detail withreference to the accompanying drawings which illustrate the structure ofthe welding apparatus of the present invention. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiment set forth herein.

FIG. 1 is a cross-sectional schematic view of a laser welding apparatusin accordance with a prefered embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of an optical systemcentrally arranged in the apparatus of FIG. 1.

FIG. 3 is a schematic diagram representing the optical path of the laserbeam through the optical system of FIG. 2.

FIG. 4 is an enlarged cross-sectional view of the further sleeverepresented in the lower part of FIG. 2 according to an alternateembodiment of the present invention.

FIG. 4 a is an enlarged cross-sectional view of the further sleeve ofFIG. 4, the cross-section being perpendicular to that of FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now initially to FIG. 1, a laser beam welding apparatus 1 inaccordance with the present invention is described. The apparatus 1comprises a main housing 2 in which are enclosed most of the constituentelements of the apparatus. The main housing 2 comprises means (notshown), such as feet for example, to be positioned on a worktable 3above a workpiece W holding tool (not represented in detail).

The main housing comprises a side opening 4 through which a laser beam 5passes, along a substantially horizontal direction, said beam beinggenerated by a remote laser source (not shown). The laser beam 5 is,directed onto a semi-transparent mirror 6 at an angle of approximately45 degrees with respect to the incident laser beam to redirect thelatter in a substantially vertical direction.

Further, a top opening 7 is provided above the back side of thesemi-transparent mirror 6 to be used, in a conventional manner, as anobservation window for the positioning of an optical sensor 200, such asa CCD camera for example The optical sensor may be connected to a signalprocessing unit 201 comprising, in particular, a processor, theprocessing unit possibly being connected to a display 202.

Following the optical path of the laser beam downwards from thesemi-transparent mirror 6 there is provided a main chamber 8, in which amovable unit 9, able to be translated in the direction of a central axisX1 is partially enclosed. The movable unit 9 is connected to the mainhousing 2 through lateral arms 10 extending in a direction parallel tothe central axis X1 and cooperating with holes 11 of supportingextensions 12, arranged on the inner surface of the main housing.Preferably, ball bearings 13 are inserted between each of the supportingextensions 12 and its corresponding arm 10 to improve a sliding movementbetween these two elements when the movable unit 9 is translated. Thevertical position of the movable unit can be adjusted with respect tothe housing, this being implemented by any suitable means, such asmicrometric screws, for example.

The movable unit comprises a centrally arranged optical system 100,radially delimited by a sleeve 101, which will be described later inmore detail. The sleeve 101 comprises two distant annular step portions16 on which bearings 17 abut, in order to maintain the position of thesleeve, in the direction of the central axis X1 with respect to themovable unit 9, and to radially guide the sleeve. An annular screw 18cooperates with a thread portion provided at the front end 19 of thesleeve 15 to tighten the bearings 17 against the corresponding stepportion 16.

A rotor 20 is directly arranged around the sleeve 101 in a stationnarymanner, the rotor being for example made in the form of a permanentbipolar magnet.

A stator 21 is concentrically arranged around the rotor 20, the statorbearing a plurality of coils 22, two of which are shown on the drawing.Thus, the combination of the rotor 20 and the stator 21 forms a motorwhose power supply means are schematically shown by reference 23. Theoperation of the motor induces a rotational motion of the optical system100, via rotation of the sleeve 101.

Further, the movable unit 9 comprises, in its lower part, a block 24 inwhich is provided a central cavity 25 comprising a first upper annularmirror 26 as well as a second lower annular mirror 27. As can be seenfrom FIG. 1, both annular mirrors 26 and 27 have a planar shape incross-section.

Conventional means are provided for accurately adjusting the respectivepositions of the mirrors 26 and 27 such as, for example a set comprisinga screw and a spring (not represented) arranged apart from thecorresponding mirror. Thus, it is possible to adjust the inclination ofthe axis of each mirror 26, 27 with respect to the central axis X1, inorder to control the quality of the laser beam before it impinges ontothe workpiece W.

The block 24 may be hold against the main housing 2 of the apparatus bythe way of a plurality of screws 28, for example.

Further, the block 24 comprises a base central opening 29 closed by acup shaped protection window 30. The function of this window 30 is toprevent the optical elements of the apparatus being spoiled by dust orplasma during the welding process. Means are also provided foraccurately adjusting the position of the protection window 30 withrespect to the central axis X1 and the annular mirrors 26 and 27, forexample by use of a screw 31.

It is to be noted that the protection window can take various forms aslong as it fulfils the requirement of being substantially perpendicularto the central rays of the laser beam 5. Thus, the protection windowdoes not play any optical role in the laser beam propagation. In otherwords, the shape of the protection window is subject to variations,enclosed within the scope of the present invention, as a function of thedirection of propagation of the laser beam 5 in the region of theprotection window, i.e. as a function of the reflecting surfacestructure.

Now with reference to FIG. 2, the rotating optical system 100 will bedescribed in more detail. The optical system 100 is schematicallyrepresented in FIG. 2, the sleeve 101 being omitted to enhance thedescription of the optical parts.

FIG. 2 shows a first tubular element 32 which is still with respect tothe movable unit 9 and comprising a plurality of radial extensions 33defining a supporting frame. In the region of the end 34 of the tubularelement 32 there is arranged a lens 35, the main function of which is tolimit the divergence of the laser beam 5.

The first tubular element 32 is partially surrounded by a second tubularelement 38, the function of which will be explained later.

The optical system 100 comprises a further sleeve 103 carrying, inparticular, an optical device 104 having a planar input surface 105 anda hemispherical output surface 106.

In a prefered embodiment of the present invention, the optical device104 is a block made of quartz, in which a planar gap, forming thereflecting surface 102, is provided. The gap may be simply filled withair and is oriented with a certain angle with respect to the centralaxis X1, in order to change the direction of an incident laser beam asshown in FIG. 1. The optical device 104 may be simply maintained byfriction inside the sleeve 103.

It is to be noted that the reflecting surface 102 may be made in anyother suitable form by those skilled in the art, without departing fromthe scope of the present invention. However, the use of a mirror may notbe as efficient as the use of a gap as regards the risk of heating dueto the high power of the laser beam used. Thus, it is clear that the useof a conventional mirror is also possible, in particular in applicationsfor which the use of a high power laser beam is not necessary.

From another point of view, the disclosed shape of the optical device104 is advantageous as regards its moment of inertia during the rotationof the optical system.

Further, the sleeve 103 houses a correcting lens 107, borne by asupporting member 108. The supporting member 108 is mechanicallyconnected to the sleeve 103 by two pivot pins (not shown) aligned toeach other in the direction perpendicular to the plane of FIG. 2. Thesupporting member also comprises two pins 109 and 110 parallel to eachother and to the direction of the central axis X1, arranged in adaptedblind holes of the supporting member.

A first pin 109 is supported in its hole by a helicoidal spring 111while the second pin 110 is held in a fixed position with respect to itshole, for example by a threading (not shown).

An annular element 112, threaded in the sleeve 103, abuts the pins 109and 110 with its lower surface. Hence, it is apparent from FIG. 2 that,if the annular element 112 is threaded down in direction of thesupporting member 108, pressure is exerted on the pins 109 and 110. Aspin 110 is fixed to the supporting member, it induces a pivoting motionof the latter while increasing the pressure exerted onto the pin 109.Consequently, the pressure exerted on the pin 109 is transmitted to thespring 111 that becomes more compressed in order to absorb the pressure.

As a result, the correcting lens 107 is tilted or, in other words, itsoptical axis X2 is rotated with respect to the central axis X1. In theabove example, the optical axis X2 is rotated clockwise, asschematically shown in FIG. 2.

The second tubular element 38 plays the part of a tool for operating theannular element 112 from outside the optical system 100. Indeed, it canbe seen in FIG. 2 that the second tubular element 38 comprises aplurality of short rods 39 protruding from its lower surface forcooperating with corresponding blind holes 113 provided in the uppersurface of the annular element 112. Thus, the second tubular element 38has to be lowered, by an operator, by compressing supporting springs 40so that the short rods 39 enter the blind holes 113. Then, and while thesprings 40 remain under compression, the second tubular element 38 isrotated to induce a rotational movement of the annular element 112 andthus tilting of the correcting lens 107. When the pressure on the secondtubular element 38 is released, the short rods 39 are released from theblind holes 113 and the annular element 112 is maintained in a fixedangular position.

The function of the correcting lens 107 is to act on the laser beam 5 toavoid the occurrence of any geometrical aberration of the image focalpoint in the welding region, i.e. to improve the quality of the imagefocal point.

For the same reason, the respective surfaces of the annular mirrors 26and 27 have to be treated very carefully during their preparationprocess. Due to the high quality of the mirror surface preparation, thequality of the image focal point is enhanced.

As apparent from FIG. 1, the optical path of the laser beam 5 throughthe apparatus according to the present invention is such that it ispossible to achieve circular welding when the optical system 100 isdriven in rotation by the motor.

Referring now to FIG. 3, the optical principles implemented in theapparatus according to the present invention will be described.

When the movable unit 9 is in its neutral position, the image focalpoint in the impact region of the workpiece W is located at FO.

Starting from this situation, the user has to make the movable unit 9translate up or down to adjust the radius value of the circle swept bythe laser beam during operation as a function of the dimensions of theworkpiece W. The image focus point is thus translated along the opticalpath of the laser beam, together with the translation of the movableunit 9. When the movable unit 9 is arranged in its highest position withrespect to the housing 2, the image focal point is located at F1′ andwhen the movable unit is arranged in its lowest position, the imagefocal point is located at F1.

Of course, the method that has just been described as regards theadjustment of the focus point position is given as an example and is notlimiting. It could be subject to variations due to a choice of adifferent number of lenses for example or a choice of lenses of adifferent nature.

Starting from the input of the optical system 100, the laser beam 5 isslightly divergent when it impinges onto the first convergent lens 35,the function of which is to decrease the beam divergence. The opticalpath extends then through the tiltable lens 107 which is convergent, itsfocal length being substantial. More particularly, the focal length ofthe tiltable lens is adapted to the dimensions of the apparatusaccording to the present invention, so as to form the image focus pointon the surface of the workpiece W.

Further, as previously mentioned, the tiltable lens 107 is able to pivotabout an axis parallel to the first reflecting surface 102 so that itsoptical axis X2 is able to be inclined with respect to the central axisX1. Thus, the quality of the image focus point formed on the surface ofthe workpiece W can be finely adjusted by pivoting the tiltable lens107, in order to avoid the formation of an ellipse-shaped focus pointfor example. This last feature is particularly advantageous since thetiltable lens 107 and the first reflecting surface 102 are rotatedtogether so that their mutual orientation remains still during theoperation of the apparatus.

Referring now to FIG. 4 and FIG. 4 a, an alternate embodiment of thefurther sleeve 103 according to the present invention, which wasdescribed in relation with FIG. 2, will be described.

More particularly, the present embodiment concerns changes in thestructure supporting the correcting lens 107 and thus in the meansprovided for the adjustment of the orientation angle lying betweenoptical axis X2 and central axis X1.

Here again, a supporting member 408 is mechanically connected to thesleeve 103 by means of two pivot pins 401 and 402 aligned with respectto each other in the direction perpendicular to the plane of FIG. 4,i.e. along the plane of FIG. 4 a.

Two elastic rings 403, 404 are provided respectively on both sides ofthe supporting member 408, each of these rings being formed of a stackof a plurality of flat rings as can be seen from FIGS. 4 and 4 a.Prefeably, the flat rings are made of metal and are welded or gluedtogether at least partly around their periphery by any adapted knownmethod.

Each of the elastic rings 403, 404 comprises two holes 405, 406traversing its thickness and located such as to be diametricallyopposed, a screw 409, 410 being arranged in each of the holes.

A first screw 409 of each elastic ring tightens the latter to thesupporting member 408 in a region of connection, the respective regionsof connection being diametrically opposed.

The second screw 410 of each elastic ring simply ensures that the flatrings remain tightened to each other and is thus shorter than thecorresponding first screw 409. All screw heads protrude from the elasticrings on their respective sides opposite the supporting member 408.

Consequently, the screw heads of a first elastic ring 403 abuts againstthe annular element 112 (as disclosed in connection with FIG. 2) whilethe screw heads of the second elastic ring 404 abuts against a step 411provided inside the sleeve 103.

Then, the functionning of the assembly formed by the supporting member408 together with the two elastic rings 403 and 404 will be described.

In a similar fashion to that described in relation with FIG. 2, when theannular element 112 is screwed in the direction of the supporting member408, pressure is exerted on the screw heads of the first elastic ring403.

Under the effect of the pressure, the first elastic ring 403 bends thuscausing the second elastic ring 404 to bend, as the supporting member408 is rigid and less prone to bending. As a result of the respectivebendings of both elastic rings 403 and 404, the supporting member 408and thus the optical axis X2 of the correcting lens 107 are inclinedwith respect to the direction of the central axis X1. More particularly,when the annular element 112 is screwed on FIG. 4, the correcting lens107 is rotated anti-clockwise.

As already mentioned above, the function of the correcting lens 107 isto act on the laser beam 5 to avoid the occurrence of any geometricalaberration of the image focal point in the welding region, i.e. toimprove the quality of the image focal point.

More generally, an important aspect of the apparatus according to thepresent invention lies in the fact that the tiltable lens 107 and thefirst reflecting surface 102 are rotated simultaneously.

The apparatus according to the present invention can be used in manydifferent applications. For example, it can be used as an examinationapparatus by using the presence of the observation window in combinationwith an optical sensor 200 as mentioned above. In such a case, the sideopening 4 of the housing 2 is not necessary as no laser beam needs to beinput in the apparatus. However, this opening 4 can be kept and used asan input for a light source in order to light the region of theworkpiece to be examined and enhance the contrast of the observationimage.

Another important advantage of the present invention lies in the factthat in order to treat a series of workpieces, the optical system can bekept rotating between two successive workpieces to be treated. The laserbeam supply means need only be stopped for the time necessary to removea treated workpiece and to position a new workpiece, which saves timefor the user.

Further conventional features can be added in the above describedapparatus without departing from the scope of the present invention. Forexample, a cooling fluid supply circuit can be provided to cool thebearings 17 as visible in FIG. 1. A device for measuring the rotationalspeed of the optical system can also be provided.

1-19. (canceled)
 20. An apparatus for generating a rotating laser beam,in particular for circular welding and/or machining workpieces, saidapparatus comprising input means for a laser beam, said laser beamfollowing an optical path through at least one optical system of theapparatus before emerging from said apparatus through an output andimpinging onto an impact region of a workpiece, said optical systemhaving a central axis and being intended at least to adjust the positionof an image focal point of said laser beam in said impact region, saidoptical system further comprising a first reflecting surface able torotate about said central axis, said first reflecting surface beingintended to redirect said laser beam into the direction of at least asecond reflecting surface intended to reflect said laser beam towardsaid workpieces, the apparatus comprising means for driving said firstreflecting surface in rotation together with said optical system so thattheir mutual orientation remains still during the operation of theapparatus, wherein said optical system comprises a rotating lens ofoptical axis arranged so as to be tiltable, such that said optical axisis able to be angled with respect to said central axis to increase thequality of the focus point on said workpieces, and that the optical pathof said laser beam goes through said rotating lens before beingredirected by said first reflecting surface.
 21. The apparatus accordingto claim 20, wherein said first reflecting surface is arranged in afixed manner in said optical system.
 22. The apparatus according toclaim 21, wherein said at least second reflecting surface is intended toreflect said laser beam toward said axis.
 23. The apparatus according toclaim 21, wherein the apparatus comprises a third reflecting surface,said second and third reflecting surfaces being of substantially planarshape in cross-section.
 24. The apparatus according to claim 23, whereinsaid third reflecting surface is intended to reflect said laser beamtoward said axis.
 25. The apparatus according to claim 24, wherein saidoptical system comprises a sleeve in which are arranged said firstreflecting surface and said rotating lens, the latter being borne by asupporting member mechanically connected to said sleeve by twodiametrically opposite pins so as to be able to be tilted, an annularelement being provided inside said sleeve abutting on said supportingmember to adjust the angle between said optical axis and said centralaxis via a threading.
 26. The apparatus according to claim 25, whereinsaid supporting member comprises two rods protruding from its uppersurface and diametrically opposed along a direction perpendicular tothat of said pins, a first of said rods being fixed in said supportingmember while the second of said rods is arranged in a blind hole andsupported by a spring.
 27. The apparatus according to claim 26, whereinthe apparatus further comprises two elastic rings respectively locatedon both sides of said supporting member, each of said elastic ringsbeing connected at a certain angle with a region of said supportingmember, the respective regions of connection of the elastic rings withthe supporting member being approximately diametrically opposed, saidsupporting member and said two elastic rings forming an assemblyarranged in abutment, on the one hand, against said annular element and,on the other hand, against a step provided inside said sleeve.
 28. Theapparatus according to claim 26, wherein a tubular element is partiallyengaged in said sleeve and is provided with means able to cooperate withsaid annular element in order to drive the latter in rotation withrespect to said central axis such that the position of the latter in thedirection of said central axis can be adjusted from outside said sleeve.29. The apparatus according to claim 26, wherein said first reflectingsurface is arranged in an optical device which has, along the directionof propagation of the laser beam, a planar input surface and ahemispherical output surface, said reflecting surface being formed by aplanar gap.
 30. The apparatus according to claim 29, wherein saidreflecting surface intersects said central axis substantially at thecentre of curvature of said hemispherical output surface.
 31. Theapparatus according to claim 30, wherein the apparatus further comprisesa protection window in the region of the apparatus output.
 32. Theapparatus according to claim 31, wherein said protection window has ashape arranged in such a manner that central rays of said laser beamintersects said protection window substantially in a perpendicular way.33. The apparatus according to claim 24, wherein the quality of saidimage focal point is able to be adjusted by the angle between saidoptical axis and said central axis.
 34. The apparatus according to claim20, comprising a housing, wherein said housing includes said laser beaminput means, the apparatus further comprising a movable unit, saidmovable unit being at least partially enclosed in said housing andcomprising at least said optical system and said second reflectingsurface, and in that said movable unit is able to be translated alongthe direction of said central axis with respect to said main housing soas to adjust its position along said central axis.
 35. The apparatusaccording to claim 20, wherein said drive means comprise a rotorarranged around said optical system in a fixed manner, a stator beingarranged in said movable unit around said rotor.
 36. The apparatusaccording to claim 20, further including an observation window allowingthe impact region to be observed.
 37. The apparatus according to claim36, wherein said observation window is associated with a vision unit.38. The apparatus according to claim 37, wherein said vision unitcomprises a camera, an image processing circuit and a monitor.